Comparison of spherical nanogold particles and nanogold plates for the oxidation of dopamine and ascorbic acid

DNA Framework-Templated Fabrication of Ultrathin Electroactive Gold Nanosheets

Generally, two-dimensional gold nanomaterials have unique properties and functions that offer exciting application prospects. However, the crystal phases of these materials tend to be limited to the thermodynamically stable crystal structure. Herein, we report a DNA framework-templated approach for the ambient aqueous synthesis of freestanding and microscale amorphous gold nanosheets with ultrathin sub-nanometer thickness. We observe that extended single-stranded DNA on DNA nanosheets can induce site-specific metallization and enable precise modification of the metalized nanostructures at predefined positions. More importantly, the as-prepared gold nanosheets can serve as an electrocatalyst for glucose oxidase-catalyzed aerobic oxidation, exhibiting enhanced electrocatalytic activity (~3-fold) relative to discrete gold nanoclusters owing to a larger electrochemical active area and wider band gap. The proposed DNA framework-templated metallization strategy is expected to be applicable in a broad range of fields, from catalysis to new energy materials.

Electrochemical sensing of dobutamine, paracetamol, amlodipine, and daclatasvir in serum based on thiourea SAMs over nano-gold particles-CNTs composite

We report in this work a one-step approach for the formation of self-assembled monolayers (SAMs) from thiourea (TU) over gold nanoparticles dispersed in carbon nanotubes (CNTs-Aunano). The fabrication of the...

Seed-mediated growth of high yield Au nanoplates with in situ generated Au clusters through galvanic replacement

A photochemical method is used to grow Au nanoplates in high yield from in situ generated Au cluster seeds through the galvanic replacement reaction. The morphology of nanoplates can be further controllably tuned by adjusting the pH, and enhanced morphology determined non-linear optics performances are obtained.

Designed electrochemical sensor based on metallocene modified conducting polymer composite for effective determination of tramadol in real samples

A novel composite for the electrochemical sensing of tramadol (Tr) was developed by the inclusion of a metallocene mediator between two layers of conducting poly(3,4-ethylenedioxythiophene) (PEDOT) polymer, in the presence of sodium dodecyl sulfate (SDS), i.e., P/mediator/P⋯SDS. Three charge transfer mediators were evaluated: ferrocene carboxylic acid (FC1), ferrocene (FC2), and cobaltocene (CC) for Tr electrocatalytic oxidation. The FC1 charge mediator showed a relatively higher current response that was assisted by the electronic conduction of the polymer film. Moreover, SDS presented a great impact, resulting in the enhancement of the preconcentration and (or) accumulation of Tr ions at the interface, leading to faster electron transfer. In addition, the practical application of the proposed FC1 composite for the determination of Tr in real urine and serum samples was successfully achieved with adequate recovery results. Very low detection limits of 18.6 nM and 16 nM in the linear dynamic ranges of 7–300 µM and 5–280 µM, respectively, were obtained at the proposed sensor. Furthermore, the simultaneous determination of Tr with common interfering species, paracetamol (APAP), morphine (MO), dopamine (DA), ascorbic acid (AA) and uric acid (UA), proved excellent, with good resolution and large potential peaks separation. The excellent characteristics of the proposed composite such as high reproducibility, good sensitivity, selectivity, anti-interference ability, and good stability enhanced its application for determination of other narcotic drugs.

Gold Nanoplates for a Localized Surface Plasmon Resonance-Based Boric Acid Sensor

Localized surface plasmon resonance (LSPR) properties of metallic nanostructures, such as gold, are very sensitive to the dielectric environment of the material, which can simply be adjusted by changing its shape and size through modification of the synthesizing process. Thus, these unique properties are very promising, particularly for the detection of various types of chemicals, for example boric acid which is a non-permitted preservative employed in food preparations. For the sensing material, gold (Au) nanoplates with a variety of shapes, i.e., triangular, hexagonal, truncated pentagon and flat rod, were prepared using a seed-mediated growth method. The yield of Au nanoplates was estimated to be ca. 63% over all areas of the sensing material. The nanoplates produced two absorption bands, i.e., the transverse surface plasmon resonance (t-SPR) and the longitudinal surface plasmon resonance (l-SPR) at 545 nm and 710 nm, respectively. In the sensing study, these two bands were used to examine the response of gold nanoplates to the presence of boric acid in an aqueous environment. In a typical process, when the sample is immersed into an aqueous solution containing boric acid, these two bands may change their intensity and peak centers as a result of the interaction between the boric acid and the gold nanoplates. The changes in the intensities and peak positions of t-SPR and l-SPR linearly correlated with the change in the boric acid concentration in the solution.

High-yield synthesis of triangular gold nanoplates with improved shape uniformity, tunable edge length and thickness

We report the synthesis of uniform triangular gold nanoplates by a modified seeded growth method. The concentration of cetyltrimethylammonium bromide (CTAB) in the growth solution and the time interval between multiple steps of growth were important factors which determined the formation of uniform triangular Au nanoplates. In addition, by further isotropic overgrowth, the thickness of triangular Au nanoplates can be finely tuned within a wide range of 10-80 nm, which at present remains a challenge using conventional seeded growth.

Gold Nanoparticles and Nanocomposites in Clinical Diagnostics Using Electrochemical Methods

Progress and development in clinical diagnostics certainly focus upon the advances in the nanomaterials, particularly gold nanoparticles (AuNPs) that offer promise to solve the biocompatible and sensitive detection systems. This paper focuses on the recent application of AuNPs in clinical diagnosis. Various important methods of AuNPs synthesis and their application in clinical detection of various biomolecules using electrochemical detection methods have been described. AuNPs alone and in various composites are also described based on the various biosensors design recently published for the detection of cancer biomarkers, proteins, bacteria, and cancer cells. The effect of AuNPs type and size in clinical detection has also been briefly illustrated.

An 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid)-immobilized electrode for the simultaneous detection of dopamine and uric acid in the presence of ascorbic acid

An 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS)-immobilized carbon nanotube (CNT) electrode was used to simultaneously detect dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA) with differential pulse voltammetry. When ABTS was immobilized onto the CNT electrode in the presence of DA, UA and 100 μM AA, the sensitivity to DA increased from 0.600 (±0.013) to 1.334 (±0.010) μA/μM in the concentration ranges of 0.90-10 μM and 1.87-20 μM, respectively, and the sensitivity to UA increased from 0.030 (±0.005) to 0.078 (±0.006) μA/μM in the concentration ranges of 2.16-240 μM and 3.07-400 μM, respectively. These findings demonstrate that the ABTS-immobilized CNT electrode attained a higher sensitivity to UA and also a wider linear range of concentrations.

Modification of Gold Surface with Gold Nanoparticles and Cyclohexyl Dithiocarbamate as a Selective Sensor for Cysteine

The self-assembly of cyclohexylamine dithiocarbamate (C6DTC) on gold (Au) and gold nanoparticles (AuNPs) was studied electrochemically using cyclic voltammetry (CV). Cyclic voltammetry was used to study the systemFe(CN)63-/Fe(CN)64-at the electrode surface of (C6DTC/Au) and (C6DTC/AuNPs). The application of the resulting chemically modified surface as a selective sensor for cysteine, among other amino acids, was investigated. Linear oxidative desorption technique was used to characterize the modified electrode that consists of the self-assembled monolayer of cyclohexylamine dithiocarbamate on gold nanoparticles deposited on Au electrode (C6DTC/AuNPs/Au). The results showed an enhancement in the oxidation peak of cysteine on the modified electrode and hence a greater sensitivity.

Detection of formaldehyde in water: a shape-effect on the plasmonic sensing properties of the gold nanoparticles

The effect of morphology on the plasmonic sensing of the presence of formaldehyde in water by gold nanostructures has been investigated. The gold nanostructures with two different morphologies, namely spherical and rod, were prepared using a seed-mediated method. In typical results, it was found that the plasmonic properties of gold nanostructures were very sensitive to the presence of formaldehyde in their surrounding medium by showing the change in both the plasmonic peaks position and the intensity. Spherical nanoparticles (GNS), for example, indicated an increase in the sensitivity when the size was increased from 25 to 35 nm and dramatically decreased when the size was further increased. An m value, the ratio between plasmonic peak shift and refractive index change, as high as 36.5 nm/RIU (refractive index unit) was obtained so far. An expanded sensing mode to FD was obtained when gold nanostructures with nanorods morphology (GNR) were used because of the presence of two plasmonic modes for response probing. However, in the present study, effective plasmonic peak shift was not observed due to the intense plasmonic coupling of closely packed nanorod structures on the surface. Nevertheless, the present results at least provide a potential strategy for response enhancement via shape-effects. High performance plasmonic sensors could be obtained if controlled arrays of nanorods can be prepared on the surface.

Synthesis of gold nanocubes in aqueous solution with remarkable shape-selectivity

This paper reports a facile method to prepare gold nanocubes with an average size length of 13 ± 2 nm, a shape selectivity >90%, and a very good reproducibility. The gold nanocubes were prepared by photocatalytic reduction of Au(III) using a cationic, water soluble porphyrin as the photocatalyst, and cetyltrimethylammonium bromide as the capping agent. The synthesis is performed in water, at pH 7, and room temperature. The nanocubes were characterized by transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and X-ray phototelectron spectroscopy. Shape selectivity for the synthesis of nanocubes is due to a different rate of growth of the (100) and (111) facets of the nanoparticles, and such control in this synthesis is achieved by careful selection of the initial gold precursor for the photocatalytic cycle.

Single-Walled-Carbon-Nanotube-Modified Pyrolytic Graphite Electrode Used as a Simple Sensor for the Determination of Salbutamol in Urine

A fast and sensitive voltammetric method has been proposed for the determination of salbutamol at single-walled-carbon-nanotube-modified edge-plane pyrolytic graphite electrode (SWNT/EPPGE) in human urine. The electrochemical response of salbutamol was determined by square wave voltammetry (SWV) in phosphate buffer solution (PBS) at physiological pH 7.2. The modified electrode showed improved voltammetric response towards the oxidation of salbutamol, and a well-defined anodic peak was observed at~600 mV with enhanced peak current in comparison to the bare electrode. Linear calibration plot using SWNT/EPPGE was obtained in the concentration range of 50 to 2500 ngml-1with sensitivity and detection limit of 2.15 nA/ngml-1and 4.31 ngml-1, respectively. The developed method has been successfully applied for the determination of salbutamol in commercial preparations and human body fluids. Fast analysis of salbutamol in human urine makes the proposed method of great interest for doping control purposes at the site of competitive games.

One-pot synthesis of triangular gold nanoplates allowing broad and fine tuning of edge length

A photocatalytic approach was used to synthesize triangular nanoplates in aqueous solution. The synthesis is based on the reduction of a gold salt using a tin(iv) porphyrin as photocatalyst, cetyltrimethylammonium bromide (CTAB) as a stabilizing agent, and triethanolamine (TEA) as the final electron donor. The average edge length of the triangular nanoplates can be easily changed in the range 45-250 nm by varying the concentration of photocatalyst, and fine-tuning of the average edge length is achieved by varying the concentration of CTAB. Study of the mechanism of formation of the nanoplates by UV-vis and by transmission electron microscopy (TEM) shows that there is a first stage where formation of 5 nm seeds takes place, further growth is probably by fusion and by direct reduction of gold onto the preformed nanoparticles. The nanoparticles formed during the photocatalytic reduction of the gold precursor show an irregular shape that evolves to regular triangular nanoplates after ripening in solution for 24 h.